How did Uncle Digory visit Narnia?

Question

In the movie, Uncle Digory used to believe Lucy's stories of Narnia and he showed the expression that he experienced Narnia before. I thought he visited Narnia through the same wardrobe when he was kid (after all it was his own mansion and old wardrobes can exist).

But, I just learned that that wardrobe wasn't in existence when he visited Narnia:

As DavidS points out (thanks muchly), the children take with them an apple, which is planted and grows a tree, from which this wardrobe is created (which I believe is the explanation as to why it can go through Narnia. This is very much a "this is why" installment to the series).

Now, the question is: How did Uncle Digory visit Narnia without the wardrobe?

Answer 1

In The Magician's Nephew, Uncle Digory's Uncle (The Magician) creates magic rings which he gives to his nephew (Digory Kirke) and his nephew's friend (Polly Plummer). These two visit a land which is like an 'in-between' land which is a forest with many pools, through which one can visit many different lands. Wikipedia describes it well:

Digory finds himself transported to a sleepy woodland with an almost narcotic effect; he finds Polly nearby. The woodland is filled with pools. Digory and Polly surmise that the wood is not really a proper world at all but a "Wood between the Worlds", similar to the attic that links their rowhouses back in England, and that each pool leads to a separate universe.

It is through one of these pools that Digory visits the newly-formed land of Narnia!

So, in answer to your question, Digory got to Narnia under the power of his Uncle's (the Magician's) rings, as well as the pools in the 'Wood between the Worlds'.

I would strongly recommend you read The Magician's Nephew as it answers this question in quite a bit of detail!

Answer 2

This is explained in The Magician's Nephew.

Digory Kirke had an uncle, Andrew Ketterley, who had a fairy godmother, Mrs Lefay:

[Andrew] "My godmother was a very remarkable woman. The truth is, she was one of the last mortals in this country who had fairy blood in her. [...] In fact, Digory, you are now talking to the last man (possibly) who really had a fairy godmother."

Before dying, she gave him a box from Atlantis which contained dust from another world:

[Andrew] "She had got to dislike ordinary, ignorant people, you understand. I do myself. But she and I were interested in the same sort of things. It was only a few days before her death that she told me to go to an old bureau in her house and open a secret drawer and bring her a little box that I would find there. The moment I picked up that box I could tell by the pricking in my fingers that I held some great secret in my hands. She gave it me and made me promise that as soon as she was dead I would burn it, unopened, with certain ceremonies. That promise I did not keep." [...]

[Andrew] "The Atlantean box contained something that had been brought from another world when our world was only just beginning. [...] Only dust. [...] If only you could get it into the right form, that dust would draw you back to the place it had come from. [...] At last I succeeded in making the rings."

Andrew made two kinds of rings: yellow and green. With the former you can go to the Wood between the Worlds, with the latter you can go from there to any world:

[Digory] "No, I don't believe this wood is a world at all. I think it's just a sort of in-between place. [...] Think of our tunnel under the slates at home. It isn't a room in any of the houses. In a way, it isn't really part of any of the houses. But once you're in the tunnel you can go along it and come into any of the houses in the row. Mightn't this wood be the same?—a place that isn't in any of the worlds, but once you've found that place you can get into them all." [...]

[Narrator] Uncle Andrew, who knew nothing about the Wood between the Worlds, had quite a wrong idea about the rings [...]. The stuff of which both were made had all come from the wood. The stuff in the yellow rings had the power of drawing you into the wood; it was stuff that wanted to get back to its own place, the in-between place. But the stuff in the green rings is stuff that is trying to get out of its own place: so that a green ring would take you out of the wood into a world.

Andrew coerces Digory and his friend Polly into testing the rings. They go to a world called Charn, where Digory awakens the malicious Queen/Witch Jadis. Digory and Polly attempt using the rings to run away to Earth, but since she is touching them, she is transported too. They attempt to take her back to Charn, but they make a mistake:

[Jadis] "This is not Charn," came the Witch's voice. "This is an empty world. This is Nothing."

Then the Lion, Aslan, creates Narnia in that previously empty world:

[Narrator] In the darkness something was happening at last. A voice had begun to sing. [...]

[Narrator] One moment there had been nothing but darkness; next moment a thousand, thousand points of light leaped out—single stars, constellations, and planets, brighter and bigger than any in our world. [...]

[Aslan] "Narnia, Narnia, Narnia, awake."